The present invention relates to vehicle wheels and, more specifically, to an improved method for producing a wheel disc adapted for use in such a vehicle wheel.
One type of conventional fabricated vehicle wheel comprises a two-piece construction having an inner disc and an outer rim. The disc includes an inner wheel mounting portion and an outer annular portion. The wheel mounting portion defines an inboard mounting surface and includes a center pilot or hub hole, and a plurality of lug receiving holes formed therethrough for mounting the wheel to an axle of the vehicle. The rim is fabricated from steel, aluminum, or other alloys, and includes an inboard tire bead seat retaining flange, an inboard tire bead seat, an axially extending well, an outboard tire bead seat, and an outboard tire bead seat retaining flange. The outer annular portion of the disc is typically secured to the inner radial surface of the rim by welding.
Some preferred materials for the disc are steel and other alloys which can be cold worked from a flat blank into the desired final shape of the disc. Using several stages of die stamping and punching, a wheel disc of sufficient dimensional accuracy and strength can be economically produced. An example of progressive die stamping to manufacture wheels discs with multi-stage, high speed transfer press equipment is shown in U.S. Pat. No. 5,568,745, issued to Daudi on Oct. 29, 1996, which is incorporated herein by reference in entirety.
In addition to stringent requirements for strength and shape of both the wheel disc and rim, an attractive styling of the wheel disc is desired. Windows are formed in a typical wheel disc in order to give the wheel a spoked appearance by forming a single spoke between each pair of adjacent windows. The windows also function to provide a flow of cooling air to brake units installed inboard of the wheel.
To further improve styling of a stamped wheel disc, cladding of various shapes and finishes may be applied to the outboard side of the wheel disc after it is assembled to the rim. The cladding shape may conform to the shape of the wheel disc or it may provide a very different appearance. Regardless of actual styling, it is preferable that enough “see-through” area remains after installing the cladding to allow sufficient air flow to cool the wheel and brake.
Recent trends in wheel styling have made it desirable to provide large windows so that the unitary spokes between windows are as small as possible. When a cladding is used, a large window size in the wheel disc provides greater flexibility in styling the cladding such that the cladding windows can be located in more arbitrary locations.
Using conventional techniques for fabricating stamped wheel discs from flat blanks, it has not been possible to obtain larger window sizes. During manufacture, the blank is typically bent over to form the outer band prior to punching the windows because if the windows were to be punched first then they would distort to an unacceptable degree during bending. With larger window sizes, a punching operation becomes increasingly difficult because of the need to provide the space to receive the slugs as they are punched out.
In order to obtain larger window sizes, other forming processes such as casting of aluminum have been employed. However, these other processes and materials are less well suited to low cost, mass production. Therefore, it would be desirable to obtain increase window sizes with a stamped wheel disc.
Co-pending U.S. application Serial No. 11/345,530 filed concurrently herewith, entitled “Disc Forming Process for Wheels with Large Windows,” teaches an improved disc forming process that enables increased window size while maintaining disc strength and avoiding distortions even though the outer band is bent over after punching the larger windows. An intermediate camming operation performs a preliminary shaping prior to final shaping with a wipe die so that the disc may be formed without introducing stresses that would weaken the disc or distorting the window shape.
A potential problem associated with both the preliminary and final shaping of the outer band is unintended undulations. Due to the presence of the large windows, cyclic variations in the radial length of the outer band may be produced. The unintended length variations can produce undulations in the final outer band that run in a direction parallel with the wheel axis and/or perpendicular to the wheel axis. When the formed wheel disc is placed within the rim for welding, any undulations parallel to the wheel axis cause the seam for welding to be wavy, making it more difficult to perform the welding operation. Undulations perpendicular to the wheel axis result in discontinuous contact between the wheel disc and rim along the seam, preventing the formation of a strong welding joint. Therefore, it would be desirable to reduce undulations.
Die stamping operations to form a wheel disc are typically performed using a series of press stations with partially finished pieces being transferred between stations. In addition to the multiple stations, each station can be set up to perform more than one compatible metal forming operation such as bending some sections of the piece while a hole in another area of the piece is pierced. In order to produce a part most economically using the least equipment and factory floor space, it is desirable to use a fabrication process needing a minimal number of stations. Manufacturing costs are also dependent upon the complexity of the forming operations performed by each set of dies, both in terms of original cost of the tooling and maintenance during the useful lifetime of the tooling. Thus, it is further desirable to find a sequence of operations to form a desired wheel disc using less complicated steps without increasing the number of stations required.